Dry, free flowing concentrate for preparing a casing packer fluid



nited States DRY, FREE FLOWING CONCENTRATE FOR PRE- PARING A CASING PACKER FLUID Sam I. Kohen, Houston, Tex., assignor to Magnet Cove Barium Corporation, Houston, Tex., a corporation of Arkansas This invention relates to compositions useful as casing packer fluids for the protection of well casings and the P like from mechanical damage and from corrosion. In one of its aspects it also relates to compositions in the form of concentrates for forming such packer fluids. In another of its aspects, it relates to a method for so protecting such casings and the like.

In the drilling and completion of wells, it is common practice to set a casing in the bore hole. The casing thus set is frequently subjected to stresses imposed upon it by shifting or settling of surrounding formations which stresses cause the casing to rupture or collapse. In other instances, the casing is subjected to corrosive salt brines or other corrosive substances which seep into contact with the exterior of the casing from subterranean brine strata traversed by the bore hole,

It has been suggested that damage to the casing due to shifting of the formations or to corrosion be eliminated or substantially reduced by disposing a so-called casing packer or hell hole fluid in the space between the casing and the surrounding formations. The benefits of such a fiuid are at least twofold. First, the packer fluid provides support for the casing and absorbslateral or transverse movements of the formations traversed by the bore hole, thereby reducing mechanical damage to the casing. Secondly, the fluid surrounds the casing to isoatent O It should be compatible with both crudeand refined oils as a base. A further and important characteristic is that the gel should be thixotropic in character so that it can be reworked into a semi-fluid condition to permit the salvage of casing in those operations warranting the same.

It is an object of this invention to provide a casing packer fluid and a method of using the same wherein a vegetable pitch soap is employed to impart the above desirable characteristics to the fluid and to an extent not heretofore known to the art.

Another object is to' provide such a casing packer fluid which can be pumped into place whereupon it sets into a semi-solid plastic gel which thereafter can be reconverted into a semi-fluid condition to permit various well operations such as recovering a casing.

Another object is to provide a casing packer fluid, and a method of compounding and using the same, in which vegetable pitch, an inorganic base and mineral oil are compounded in such a manner that the rate of formation of, and the ultimate strength of, the resulting gel can be controlled, and 'if desired, considerable weight suspending ability and thixotropy imparted to the gel] Another object of this invention is to provide a casing packer fluid which employs a soap of vegetable pitch formed in situ in a mineral oil by the oil extracting vegetable pitch from a solid carrier for reaction with a base dispersed in the oil.

Another object is to provide a casing packer fluid, and

l a method of using and forming the same, in which expanded perlite is employed to impart some initial viscosity to a mineral oil phase to assist in preventing settling of weighting material therein until the oil phase can be gelled by a soap of a vegetable pitch formed'in situ late it from corrosive brines and other fluids occurring in 1 surrounding strata.

To satisfactorily yield one or both of the above benefits and alsovto facilitate its use without unnecessarily interfering or delaying other well operations, a packer fluid desirably should have several characteristics. Amongthese are that the fluid should form a gel, upon standing I quiescent, of considerable strength such that the fluid assumes a semi-plastic solid state. In order not to unnecessarily delay other well operations and since the packer fluid must be pumped into place behind the therein.

Another object of the invention is to provide a dry, free flowing composition for use in making up a casing packer fluid and in which a normally tacky vegetable pitch is dispersed on a solid adsorbent, particularly perlite, to render the same dry and free flowing, the adsorbent also serving to impart initial viscosity to an oil phase upon formulation of the packer fluid.

Other objects, advantages and features of this invention will be apparent to one skilled in the art upon a consideration of the written specification and the appended claims.

Generally, one aspect of the concept of this invention involves the use of vegetable pitch in combination with packer composition.

taminants such as cement, fresh water, salt water and the like, and it should be resistant to elevated temperatures.

Further, the casing packer fluid and the gel formed therefrom should be able to support weighting materials,

such as barite, and still retain good gelation properties.

an inorganic, substantially water-soluble base for reaction to form a soap of the vegetable pitch in a mineral oil phase to thereby convert such phase into a gel having thixotropic properties. The concentration of the vegetable pitch relative to the oil phase and that of the inorganic base relative to the pitch are controlled and proportioned so that the resulting mixture remains pumpable for a predetermined time whereupon it sets up, also within another predetermined time, into a stable, semiplastic gel having suflicient strength to serve as a casing The concentration of vegetable pitch relative to the oil phase can also be controlled to give such resulting mixture improved weight-suspending and thixotropic qualities.

As another aspect of this invention, it has been found that the vegetable pitch can be dispersed upon a particulate adsorptive material, particularly perlite, to provide a dry, free flowing concentrate. This concentrate when mixed with the oil phase readily has the pitch extracted therefrom by the oil phase for reaction with the inorganic base. Further, the particulate adsorbent imparts an initial viscosity to the mineral oil to assist in retarding settling of weighting material which may be dispersed in the oil. In this manner, there is not only provided a dry, free flowing mixture or concentrate capable of being bagged and easily used in the field to make up the desired packer fluid butalso. one in which the adsorbent itself at leastinitially. imparts desirable. properties to the packerfluid.

In accordance with this invention, a preferred formula for formulating a dry, freeiflowing concentrate for use in making up a packer fluid is as follows:

FORMULA I Ingredient: Parts by weight Vegetable pitch 250 1 Perlite 1.7

Also, suifi cient diphenylamine should be added to prevent combustion of this formula when stored in the dry state. About 50 grams of diphenylamine per 100 lbs. of

pitch is satisfactory.

For the packer fluid, a preferred formula is:

FORMUL A II While the ingredients of Formula I can becombined in a number of different manners to yield 2. dB, free flow-.

ing concentrate, it is usually preferred that the vegetable pitch be heated to a temperature sufficiently high to render it fluid, e.g., a temperature within a range'of 300 to 500 F., preferably at a temperature in the upper part of this range since higher temperaturespermit a decrease in the amount of perlite employed and causes more uniform spreading of the pitch onjthe perlite. The heated pitch is then pumped or poured gradually into mixing equipment into W hich theperlite has previously been disposed. By following suchprocedure, there results a dry, free flowing concentrate which can be'easily-bagged, and upon shippiugto the field is readily mixable with mineral oil, an inorganicbase, and, if desired, weighting material to form the desired packer fluid. In preparing such packer fluid, the concentrate is preferably added to the oil along with the requisite amount of inorganic base. These ingredients should be thoroughly mixed for a'period of time, e.g., one to two hours, before any weighting material is added to the fluid. Such premixing assures-thorough dispersion of the active ingredients in the mineral oil to impart an initial viscosity thereto to help support the weighting material until the oilis gelled and also to produce a uniform product of good gelation properties.

VEGETABLE PITCH The principal role of this ingredient in the packer fluid is to impart, upon reaction with the inorganic-base, gel strength to the mineral oil. Not only does the gel strength resulting from'the reacted pitch provide for adequate suspension of weighting material in the packer fluid but the vegetable pitch itself initially aids in this regard. In other words, the vegetable pitch prior to the formation of any substantial gel, acts to increase the mineral oils capacity to suspend weighting material.

The vegetable pitch .can be used in a concentration sufficient that upon reaction of the pitch with the inorganic base, the oil phase becomes a gel having an ultimate A.P.I. shearometer value of at least 20, and preferably at least 60 square feet. Also the concentration of vegetable pitch should be high enough that the ability of the resulting packer fluid to suspend Weighting material, where such is used, and to be reworked (thixotropicity) is acceptable. Such a concentration of pitch will usually fall within the range of 10 to 30, preferably 15 to 25, pounds per barrel of the final packer fluid. As will be demonstrated more fully below, increasing the concentration of vegetable pitch employed increases the rate at which the packer fluid approaches a desired minimum gel strength, i.e. at least 20, and preferably at least 60 on the A.P.I. shearometer scale. This, of course, assumes that adequate amounts of inorganic base are employed with the vegetable pitch to substantially convert the active ingredients thereof into a soap. In this sense then, the concentration of pitch can be chosen from the above range so that with a given excess of base present, the gel timecan be controlled. However, even then the concentration should be sufficient to give desired weight-suspending and reworking characteristics to the resulting gel,

In general, the higher molecular weight fractions of animal fats, vegetable oils, tall oils and derivatives thereof, can be employed in accordance with this invention, with vegetable pitch being preferred. The higher molecular weight fraction is derived from crude animal fats, vegetable oils or tall oils by fractional distillation or'solvent extraction to remove the lower molecular weight substances, such as the ordinary fatty acids, and thereby yield a bottoms product of relatively higher average molecular weight than that of the original crude oil or fat. The so-called pitches, including vegetable pitch, tall oil pitch, ebony fat and derivatives (e.g. amine or nitrile) thereof are especially desirable. The vegetable pitches employedin accordance with this invention are commercially available from various sources. and are identifiedin the trade by the term vegetable pitch. The'yare tacky, viscous, dark brown materials commercially produced from cotton seed, corn, and soybean oils, They may also containminor amounts of constituents from coconut and peanut oils, and from animal fats and oils, such as tallows and greases. The crude vegetable oil starting material consists mainly of fatty acid triglycerides, with minor amounts of sterols, vitamins, antioxidants, pigments, hydrocarbons, alcohols, and ketones. The crude oils also contain varying amounts of free fatty acids.

In accordance with one process for producing commercial vegetable pitches, the crude vegetable oil starting material is treated with aqueous caustic to remove the free fatty acids and other non-glyceride material. The thus removed reaction product, called raw soapstock, consists of soap, oil and non-glyceride material. The raw soapstockis treated with sulphuric acid or the like and the soaps are converted to freefatty acids and the product, called acid soapstock, consists of fatty acids, oil, and nonglyceridernaterial. The term oil is, of course, used to designate the fatty acid triglyceride. In general, the composition of vegetable oils and acid soapstoek is as follows:

The vegetableoils, or the acid soapstock s, or both, are passed through a high-pressure continuous splitter. In the splitter, these materials are intimately mixed with water and steam at about 500 F. at 760 p.s.i. The water reacts with the glycerides to form free fatty acids and glycerine, which are separated. The resulting crude fatty acid fraction contains approximately 2% unsaponifiables, 4% glycerides and 94% free fatty acids. This fraction is then fed to a continous fractionating still, where approximately 80% of the fraction is distilled overhead as fatty acids while the remainder is continuously removed from the bottom of the still as still vegetable residue. The distillation is conducted at 2-5 mm. pressure and at a temperature of about 510 F., with a very small percentage of steam being injected into the base of the column. The average time during which the residue is subjected to these conditions is about four hours.

As mentioned above, vegetable pitch can be derived from cotton seed, corn and soybean oils. Each of these oils can be separately refined as above described to provide individual still vegetable residues or they can be premixed to form a composite feed resulting in a compositeresidue. In any event, it is the usual practice to use a mixture of the residues from these three oils as a feed for the pitch producing process.

Various vegetable pitches are produced by further stripping the mixed still residues in a batch still at 2-5 mm. pressure and at 480 F. for about eight hours. The stripping is continued, with removal of lighter overhead products, until the pitch or bottoms have the desired specifications. In one instance, vegetable pitch 250 is provided by continuing the distillation until the bottoms have a viscosity of 9-19 seconds at 165 C. in a Zahn G-5 cup. A lighter pitch can be obtained by stopping the stripping while the bottoms have a viscosity 8.5- seconds at 125 C. in a Zahn G-5 cup.

In the usual case, between 20% and 25% of the original still residue is removed as an overhead product of the batch distillation to produce the vegetable pitch. The sterols, hydrocarbons, alcohols, antioxidants, pigments, aldehydes, ketones, etc., which are originally present in the still residue are carried over to a certain extent to appear as a part of the pitch or bottoms product of the batch distillation. A goodly proportion of the original percentage of these materials will be degraded or converted to other forms in the various processing steps. Under the conditions of distillation, particularly of the batch distillation, the unsaturated fatty acids will polymerize and some fatty acids will be decarboxylated. Some fatty acid anhydrides and lactones will also be formed.

Thus, corn, cottonseed and soy oils contain relatively large proportions of unsaturated fatty acids. When treated by the above process, these acids polymerize, especially during the high-temperature distillation and stripping steps. This polymerization seems to be of importance in giving these products the qualities desired here, since it results in increasing the quantity of higher molecular weight (polymeric) materials present. g

A typical pitch which has been found to be .excellent has the following typical composition:

VEGETABLE PITCH 250 Triglycerides, anhydrides and lactones 40% minimum.

This particular pitch has a viscosity (Zahn G orifice) within the range of 9 to 19 seconds at 165 C. It contains I about 0.5% of moisture and volatile matter.

Another vegetable pitch which is obtained in the same general manner as vegetable pitch 250 but which is less preferable and contains less polymerized acids and more unsaponifiable material, has a typical composition as follows:

VEGETABLE PITCH 150 Triglycerides, anhydrides and lactones 40% minimum.

It has a viscosity (Zahn G orifice) between 8.5 and 10.0 seconds at 125 C. Its moisture and volatile components amount to about 0.5

ADSORBENT The adsorbent used to form a dry, free flowing concentrate with vegetable pitch should have suflicient adsorptive power to permit adsorption thereon of the pitch to form a dry, free flowing concentrate and, of considerable importance, readily giving up the pitch to mineral oil when dispersed therein. Thus, with some adsorbents, the pitch may be so strongly adsorbed, particularly in minute pores of the adsorbent, that it is only very slowly given up to the mineral oil to become soluble therein. While such types of adsorbents can be employed to form the dry concentrate, it is obvious that they will require extended mixing in order to disperse the vegetable pitch in the mineral oil; More preferred adsorbents not only form a dry, free flowing concentrate but readily give up the pitch to the mineral oil. The preferred adsorbent is expanded perlite, a well known product. It has the properties of not only quickly releasing the vegetable pitch to the mineral oil without excessive stirring or heating (in fact,

the pitch is released readily at 32 F.) but it also has a tendency to float or remain suspended in the oil phase to produce a uniform product. To form a dry free flowing concentrate it is preferred to use perlite fines as the adsorbent. Moreover, the perlite will contribute some viscosity to the oil phase thus assisting in the initial support of weighting material until gelation occurs.

Adsorptive clays can also be used as a complete or a partial substitute for the perlite. Among these may be mentioned filter clay, diatomaceous earth, attapulgite, silica flour, oyster shell flour, bentonite and barite. Some of these, such as silica flour, are much poorer carriers and larger amounts thereof will have to be used than is used in the case of perlite. Others, such as filter clay, may have an excessive adsorptive power so that considerable mixing is required to cause them. to give up the pitchto the oil phase. For these reasons, these adsorptive clays are not as preferred as the perlite.

The amount of adsorbent to be used should be suflicient to render its mixture with the pitch dry and free flowing and also to impart an initial viscosity to the oil phase. It is preferred that the adsorbent be selected so that the Weight ratio of pitch to adsorbent will be between the ratios of 1 to 5 and 1 to 1.5. In the case of perlite, the amount employed should be that required to give a pitch to perlite weight ratio of 35 to 60., Preferably, such weight ratio should be at least 1 to 1.5 and preferably between the ratios of 35 to 52.5 and 35 to 100.

By using amounts of perlite in the upper part of this range, there results a blend which is not only sufliciently dry and free flowing to package satisfactorily, but also one in which there is suflicient perlite per final barrel of strong in character.

packer fluid to cause enough viscosity to retard the settling of weighting material until gelation occurs.

INORGANIC BASE The inorganic base which is mixed with the pitch and mineral oil to form a soap is selected from those which are substantially water-soluble and which are relatively Preferably, such base is selected from the group consisting of the alkali metal hydroxides,

be named sodium, potassium and lithium and yet it terms of carbonates, andadmixtures thereof" and barium hydroxide. Among compounds falling within such group may hydroxide; sodium, potassium and lithium carbonate; as well as the oxides thereof which hydrolyze in solution to form the corresponding hydroxide. Of these compounds, sodium hydroxide (caustic soda) is greatly preferred.

The concentration of base employed should be such as to be at least chemicallyequivalent to the vegetable pitch and, preferably, the concentration should be considerably in excess of such equivalent amount (e.g. 2 to 6 times). It has been found that with a given concentration of vegetable pitch employed, the amount of base plays an important role in determining howlong the packer fiuid must remain quiescent before it gels so as a to be unpumpable and before it achieves its ultimate gel strength. Thus, with increasingeoncentrations of, base, the gel formation rate increases. With lower concentrationsof base, the gel formation rate is relatively slow even though the same ultimate gel strength of the packer fluid will be achieved with both low and high concen 'trations of base as long as the amount of base is at least that chemically equivalent to the vegetable pitch. Stated 'in another manner, as long as a sufficient total of base.

is employed to completely react with the vegetable pitch, increasing the concentration of base affects the gelrate but not the ultimate gel strength. I

In accordance with this invention, the concentration of base employed is selected or controlled-relative.tothe amount of vegetable pitch employed, so that it is not "great'enough so the packer fiuid' will gel or increase in viscosity as to become unpurnpable within the. time which is required to pump the packer fluid behind the casing gel having an A.P.I. shearometer value of at least 20, and preferably at least 60, in a desired time after the pumping stops, say less than 48 hours. Reduced to viscosity, the pumpable range of the fluid is generally taken as any viscosity below 100 poises.

' Desirably, the base concentration is selected so that. the packer fluid achieves 35 to 50 percent of its ultimate gel strength in one-half to one hour and substantially its ultimate gel strength within one week.

In the practical use of the packer fluid of this invention, it has been found that when sodiumhydroxide is employed, a concentration to yield the above desired setting times will fall within the range to 25, preferably to 25, pounds per barrel of final packerffluid. For bases which are of lesser strength than sodium hydroxide, their concentration can be increased in inverse proportion to the strength thereof.

In a preferred manner of compounding the packer fluid of this invention, the base is first dissolved in water to form, for example, a 40% solution. The aqueous solution is added to the solution of pitch in the oil as above described.

OIL PHASE The packer fluid of this invention can be compounded with either refined or crude oils. The amount of oil to be employed will be such that with the other ingredients of the packer fluid, there will be provided a barrel of packer fluid.

While a dry, free flowing concentrate is preferred to be used in accordance with this invention, it is possible to form a liquid concentrate by dispersing or dissolving the vegetable pitch in a mineral oil such as diesel-oil. Other oils such as kerosene, crude oil, gas oil and the like can be employed provided that the amount of water they contain is limited to prevent dilution and thinning. The amount of oil to be employed in forming the liquid concentrate should be at least enough to render the vegetable pitch fluid so that the concentrate can be poured and handled at ordinary temperatures. One satisfactory concentration is 50% by volume each of vegetable pitch and diesel oil.

is great enough that'the fluid will setinto a Fluid 1 consists of volume percent liquid concentrate,

25"28 API, Kansas.

8 EXAMPLES The following examples will illustrate several Ways in which the principles of this invention have been applied and will demonstrate the unique advantages thereof.

Example 1 as set forth in Table I, as follows:

TABLE I API Shearometer Value, Lb./10QSq. Ft.

Setting Q Time, Fluid 1 Fluid 1 Fluid 1 Fluid 1 Fluid 1 Fluid 1 Fluid 1 Minutes Iil ns Pigs P255 Pll l/rs Pl tyis 1231;; 5 o 5 sit sait obi. Fre h rm n bhl. Water "Water Cement Water Water- Barlte 20 0 .0 O 0 7. 5 9 30 0 16 7 10 16 13 50 7 22 18 24 28 28 60 i1 30 30 40 35 38 60 20 35 35 45 35 40 60* 30 50 50 50 60 60 7 6G 60 60 48 6O 4 volumepercent of 50 percent by weight aqueous caustic soda solution, 76 volume percent of Arbuckle crude 011,

trate was a mixture of- 50 volume percent each of vegetable pitch 250 and diesel oil. Fluid 1 was mixed by adding'the liquid concentrates and the caustic soda solution to the crude oil followed. by sufiicient stirring to assure an intimate admixture. The resulting mixture was then divided into a sutficient number of portions to provide one for each time value, which were allowed to stand atroom temperature until the respective various times had expired. Thereupon, the API shearometer value was immediately determined in accordance with API Code 29. Where the tests involved the specified contaminants, the latter were added before the mixing was completed and the above procedure followed in determining the shearometer values at the indicated times. It will be noted that the shearometer equipment employed had a scale which extended only to a reading of 60. Therefore, shearometer values reported as 60 actually were in an undetermined excess of 60.

The efiect of these contaminants may be commented on as follows:

(a) Salt water.-Salt water in 1% and 5% concentrations seems to cause a slower gelation rate; however, the final gel strength after 24 hours is the same as the fluid without the salt contamination.

(b) Cement.-Cement also seems to slow the gelation rate but does not afiect ultimate gel strength.

(0) Fresh water.--Increasing the fresh water invasion up to 5% appears to decrease the gel rate but to have no effect upon the 24-hour gel strength. In this connection, a further test was run in which fresh water was allowed to remain in contact with the packer fluid for over 16 hours. Only a very minor surface solubility was noted. It did not upset the strength of the gel.

(d) Weighting materials-In the last column of Table I, the packer fluid was weighted to 10 pounds per gallon. The weighting material apparently lowers the rate of gel formation but does not reduce the final gel strength. The addition of the weighting material increased the viscosity from 267 centipoises to above 300 centipoises but the fluid was still well below the limits of pumpability. Settling of weight material was checked at both room temperature and F. over 24 hours and no weighting material was found to have settled.

In such fluid, the liquid concem,

7 Example 2 One of the unusual features of the packer fluid of this invention is its thixotropic character which permits it to be reworked. In other words, the fluid will set up into a gel but thereafter can be returned to a pumpable state by agitation. Upon ceasing such agitation, the fluid will again set up into a gel. This is demonstrated 1 In these tests, a fluid made up in the same manner as Fluid 1 of Table I was employed. Tests conducted at 150 F. on a Halliburton cement consistometer.

In performing these tests, a sample of the packer fluid was allowed to remain quiescent for the time indicated in Table II. Its consistency was then measured and thereupon the sample was permitted to stand for the additional time noted. It will be seen that there is an increase in consistency after each setting interval but that the fluid will break down to be within the limits of pumpability upon applying force thereto. This same phenomenon was noted at room temperature.

Example 3 To demonstrate that the fluid of this invention does not start gelation while agitation is maintained, a sample of the fluid which was made up in the same manner as Fluid 1 of Table I was stirred for the times indicated in Table III. At the end of each interval of time, the viscosity of the fluid was immediately measured and was as shown in the table. It will thus be seen that the viscosity does not increase significantly while the fluid is being stirred.

To demonstrate the effect of base upon the formation of gels, a plurality of samples of diesel oil were made up with each containing 20 pounds per barrel of vegetable pitch 250. To these samples, the various portions of caustic soda solution shown in Table IVa were added and the A.S.T.M. penetration determined after the samples had been thoroughly mixed and allowed to stand for 24 hours. All penetration tests were run in accordance with A.S.T.M. D-217-47T of October 1947. Since shearometer data previously reported as 60 actually were in an undetermined excess of 60, A.S.T.M. penetration values are reported hereafter. In this table, the caustic soda is given in terms of a solution thereof containing 50 weight percent each of sodium hydroxide and water. It will be noted from this table that the gelation rate increases rapidly with increasing concentrations of caustic soda. Accordingly, it will be seen that by varying the amount of caustic soda employed, the gelation rate can be controlled.

TABLE Iva Caustic soda solution concentration:

A.S.T.M. enetration, mm., 4 hours 0 lb./bbl 446 10 1b./bbl 44 20 lb./bhl 377 25 lb./bbl 359 30 lb./bbl 326 The effect of varying relative concentrations of vegetable pitch and caustic soda is noted in Table IVb. In running these tests, the vegetable pitch was first dissolved in diesel oil to make a 50 volume percent solution. This solution was then added to the diesel oil base after which the caustic soda was brought in.

TABLE IVb Formula (by vol. percent) Ability Gelling to Sus end Rework- Time Weigh ing ability V. Pitch Caustic Diesel Material Soda 1 Oil 2 93 Too slow 4 91 Good. 6 89 Poor. 8 87 2 88 4 86 Good. 6 84 Too fast Percentages shown are volume percent of a 50% weight percent solution of caustic soda.

It will be noted from Table IVb that decreasing the concentration of vegetable pitch to too low a value, with low concentrations of caustic soda, excessively slows the gelling time. This can be in part corrected by increasing the concentration of caustic soda but even when this is done, the packer fluid exhibits a poor ability to suspend weighting material and poor thixotropic characteristics. Thus, it is shown that the vegetable pitch plays an important role in imparting weight suspending and thixotropic characteristics to the packer fluid and that when these properties are desired, the minimum concentration of vegetable pitch should be suflicient to give the fluid these properties to the extent desired. On the other hand, when the vegetable pitch concentration is selected so that the weight suspending ability and the thixotropic character of the fluid are satisfactory, then the base concentration can be selectively varied to control the gelling rate and, further, it will be seen that the concentration of pitch can be varied above such minimum concentration to also control the gel. rate. Thus, either or both the pitch and base concentrations can be varied to control the gel rate provided the minimum pitch concentration is maintained as aforesaid. Of course, if the packer fluid is not to be weighted or reworked, greater latitude is permissible in the variation of pitch concentration.

In arriving at the comments set forth in Table IVb, it was considered that the packer fluid should develop from 30% to 50% of its total gel strength in one-half to one hour, with total strength accomplished in one week. Obviously, the tests marked with a gel time as Too slow or Too fast would be satisfactory if another criterion of gelling time were adopted and in some circumstances, packer fluids having such characteristics may be acceptable.

Example 5 A series of tests were run to demonstrate the effect of 11 vegetable pitch concentration on the ultimate gel strength of the packer fluid. These are reported in Table V:

1 Added as a dry concentrateiormed by dispersing vegetable pitch 250 on perlite in the pitch-to-perlite ratio of 862100 (by weight).

In performing these tests, the vegetable pitch dry concentrate was added to diesel oil and then 15 pounds per barrel of sodium hydroxide and 15 pounds per barrel of water were added as an aqueous solution to the pitchoil mixture. The samples were thoroughly stirred and then allowed to stand for the times indicated and then the A.S.T.M. penetration measured.

It is interesting to note that Table V indicates that when the vegetable pitch is added in combination with perlite, the ultimate gel strengths of the packer fluid are increased over and above those exhibited by packer fluids containing equal amounts of the vegetable pitch but having no perlite therein.

From the foregoing it will be seen that this invention is one well adapted to attain all of the ends and objects liereinabove set forth, together with othenad antages which are obvious and which are inherent to "die com,- position and process.

It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations. This is contemplated by and is within the scope of the claim.

The invention having been described, what isclaimed A dry, free flowing concentrate for preparing a casing packer fluid comprising vegetable pitch dispersed on expanded perlite, said perlite being present in an amount suflicient to render the resulting admixture dry and free flowing and to provide a pitch to perlite weight ratio Within the range of 1:5 to 1:15.

References Cited in the file of this patent UNITED STATES PATENTS 2,616,850 Browning Nov. 4, 1952 2,625,512 Powell Jan. 13, 1953 2,678,697 Fischer et a1 May 18, 1954 2,683,690 Armentrout July 13, 1954 2,695,669 Sidwell Nov. 30, 1954 2,728,395 Howard Dec. 27, 1955 2,734,861 Scott et al Feb; 14, 1956 2,793,996 Lummus May 28, 1957 

